Pulp Paper & Logistics
L AESSEALOGISTICS 11
multiple-effect evaporator is 100 gallons per minute, or 52 million gallons per year. Water infiltration into the evaporator must be reheated and evaporated. The energy consumption to achieve this is 50,000 MMBtus – which costs more than £400,000. Yet the fact is that simply
replacing gland packing or single mechanical seals with modern double-mechanical seals and a water management support system not only eliminates costly leakage but also improves pump reliability – it reduces the amount of seal flush water required to just a few gallons a year. With dual mechanical seals, one of the two faces seals towards the process fluid and one to atmosphere, with a barrier space between the two. Like single seals, these require a constant, consistent flow of fluid (often water) to ensure the seal faces operate efficiently and dry-running does not occur. This is where the water management support system comes into play. Using a process known as thermosiphon, the support system supplies clean, cool water to the barrier space between the double seals at a pressure higher than
the product pressure, ensuring that a consistent, stable and clean fluid film keeps the seal faces cool and lubricated. As the mechanical seals generate heat, the hot water in the barrier space rises to the tank and its heat is radiated to the atmosphere, allowing the cooler, denser water to sink back down to provide cool lubrication to the seal faces. The flush water is constantly
recycled, flowing across the seal faces in a continuous loop and reducing leakage to the absolute minimum – roughly one teaspoonful a day of water is lost, in the form of vapour.
Cost should not be a barrier It might be argued that cost should never be the first consideration for companies that want to live up to their commitment to the International Standards Organisation ISO-14001 Standard for environmental management systems and ISO-50001 Standard for energy management systems. But even those with an understandably close eye on the bottom line should consider the savings that can be accrued by installing the correct dual seal and support system. From an annual
Double mechanical seals contain the coolant medium
operational budget they could subtract: • The cost of energy to heat and
cool external flush water – one paper mill reduced energy use by 50,000 MMBtu, leading to savings of more than £400,000 and a return on investment of less than four months simply by reducing the amount of water that needed to be evaporated off. • Equipment costs for the
frequent repair or replacement of gland packing, failed bearings (caused by water ingress as a result of seal leakage) and, in worse case scenarios, pump shafts or sleeves damaged by the friction of gland packing. • Routine and unscheduled
David Amory: “There remains an unwillingness by some companies to properly investigate operational changes to tackle excessive water consumption and waste”
maintenance engineer costs – this sealing technology is almost maintenance-free and causes
no damage to bearings or pump shafts. • Effluent charges for the
discarded water. The operational and financial
benefits of upgrading to more environmentally-sustainable sealing technology is more easily quantified than the enhanced reputation that comes from being able, not just to declare a commitment to the global effort to conserve water, but to evidence it. That is surely a contribution to the future of our planet that no company in any industry should shy away from. The CDP perhaps puts it most succinctly: “Business-as-usual water management is no longer an option.” • David Amory is global head of
marketing for AESSEAL. Website:
www.aesseal.co.uk
May/June 2019
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